A nuclear fusion plant using as fuel deuterium (D) and tritium (T) requires a tritium removal facility that treats the exhaust gas from the building facility in which a nuclear fusion reactor and the like are placed. This is because the tritium contained in the exhaust gas is a radioactive substance, and hence even a slightest amount of the tritium is not allowed to be discharged to the outside of the facility. In the tritium removal facility, the exhaust gas from the building facility is made to pass through a catalyst layer, thus the tritium-containing hydrogen is combusted into water, the resulting water component is removed and collected, and thus an exhaust gas in a clean condition is discharged.